1. Field of the Invention
The present invention pertains to the field of acid sludge disposal and in particular to a process for disposing of acid sludge by converting the acid sludge into a useful compound, specifically asphalt.
2. Description of the Prior art
Because of the huge volume of used crankcase oil from vehicle engines and the oil shortage, an oil recycling industry has grown up. In the prior art, oil recycling generates a toxic byproduct called acid sludge. The volume of acid sludge generated in the recycling process is approximately 20-30% of the volume of the waste oil input. In the prior art, this acid sludge was dumped. However, it is very acidic and it contains many heavy metals and other toxic compounds which are harmful to the environment. Further, acid sludge is not biodegradable. Therefore a need has arisen to process the acid sludge to either eliminate it or convert it to a useful product.
Due to the substantial environmental concerns relating to acid sludge disposal, it is deemed desirable to have a process to convert acid sludge into an intermediate sludge that can be used to create bituminous compounds such as asphalt. Such a process would have far reaching economic and environmental importance. Specifically, the environmental and ecological pollution which results from acid sludge disposal would be reduced.
Acid sludge is a waste product produced by waste oil re-refineries. In the process of re-refining waste oil, one of the goals is to achieve an oil having the qualities of virgin oil.
One method of refining used oil to the quality of near virgin oil requires treating the oil with sulfuric acid. Sulfuric acid is added to oxidize and remove carbonaceous impurities, metal components and other oxidizable materials from the used oil. The addition of sulfuric acid causes a phase separation to occur in which there is generated a layer of relatively pure oil and a layer of acid sludge. The acid sludge settles and is removed. In this used oil refining process, the acid sludge is approximately 5% by volume of 98% sulfuric acid and has a pH less than 2 and typically a pH of 0.1. Consequently, this acid sludge is highly acidic, is considered toxic, and is not biodegradable. Disposal of this sludge is increasingly regulated by the environmental protection agencies of most federal and state governments. In addition, during these re-refining processes, large volumes of acid sludge are produced. The volume of acid sludge produced is approximately 0.25 gallons per gallon of used oil. In the years preceding 1980 this amounted to over 2 million tons of acid waste per year. Today, the volume of acid sludge may even be greater, but this is unclear.
Traditional methods of acid sludge disposal are landfill, incineration, acid recovery, neutralization, and disposal to water. These disposal options have a number of drawbacks. For example, as much as 30 to 50% of the acid sludge is water soluble. Therefore if the acid sludge is disposed of in a landfill, components of the sludge can leach into the water table and cause hazardous health conditions. In addition, incineration and neutralization of acid sludge produce toxic gaseous emissions to the atmosphere. These emissions include sulfur and sulfur dioxide which are leading causes of acid rain which is causing great damage to Canadian, English and Scottish forests. Acid recovery from the acid sludge is too expensive on the small scale and the high transportation costs make justification of a centralized location very difficult. Finally disposal to waste water can only be practiced where high volume waste water treatment facilities are available for dilution.
These traditional methods of disposal are very detrimental to the environment. In addition these traditional methods are becoming more and more costly as the regulatory requirements governing them increase.
There are prior art processes which combine acid sludge with other compounds to produce asphalt. (Schneider U.S. Pat. Nos. 4,238,241 and 4,331,481). These processes involve adding the acid sludge to pre-existing asphalt or to a mixture of asphalt and aggregate. The acid sludge used is only a small fraction of the end product. Therefore, these processes fail to use significant amounts of the acid sludge and, consequently, they do not significantly decrease the amount of acid sludge in existence.